What do urologists do ?

so i went to the doctor becuzz i thought i had a UTI.. the results came back negative so the doc sent my urine to the lab and if that comes back negative i have to do to a urologist so what will they do? if i have other UTI symptoms? and what if they dont catch what is wrong with me!!?!?!?!? i dont really wanna die!!! so someone plzz help